UninitializedValues.cpp revision ef8225444452a1486bd721f3285301fe84643b00 
1//==- UninitializedValues.cpp - Find Uninitialized Values -------*- C++ --*-==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements uninitialized values analysis for source-level CFGs.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/AST/ASTContext.h"
15#include "clang/AST/Attr.h"
16#include "clang/AST/Decl.h"
17#include "clang/AST/StmtVisitor.h"
18#include "clang/Analysis/Analyses/PostOrderCFGView.h"
19#include "clang/Analysis/Analyses/UninitializedValues.h"
20#include "clang/Analysis/AnalysisContext.h"
21#include "clang/Analysis/CFG.h"
22#include "clang/Analysis/DomainSpecific/ObjCNoReturn.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/Optional.h"
25#include "llvm/ADT/PackedVector.h"
26#include "llvm/ADT/SmallBitVector.h"
27#include "llvm/ADT/SmallVector.h"
28#include "llvm/Support/SaveAndRestore.h"
29#include <utility>
30
31using namespace clang;
32
33#define DEBUG_LOGGING 0
34
35static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
36  if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
37      !vd->isExceptionVariable() && !vd->isInitCapture() &&
38      vd->getDeclContext() == dc) {
39    QualType ty = vd->getType();
40    return ty->isScalarType() || ty->isVectorType();
41  }
42  return false;
43}
44
45//------------------------------------------------------------------------====//
46// DeclToIndex: a mapping from Decls we track to value indices.
47//====------------------------------------------------------------------------//
48
49namespace {
50class DeclToIndex {
51  llvm::DenseMap<const VarDecl *, unsigned> map;
52public:
53  DeclToIndex() {}
54
55  /// Compute the actual mapping from declarations to bits.
56  void computeMap(const DeclContext &dc);
57
58  /// Return the number of declarations in the map.
59  unsigned size() const { return map.size(); }
60
61  /// Returns the bit vector index for a given declaration.
62  Optional<unsigned> getValueIndex(const VarDecl *d) const;
63};
64}
65
66void DeclToIndex::computeMap(const DeclContext &dc) {
67  unsigned count = 0;
68  DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
69                                               E(dc.decls_end());
70  for ( ; I != E; ++I) {
71    const VarDecl *vd = *I;
72    if (isTrackedVar(vd, &dc))
73      map[vd] = count++;
74  }
75}
76
77Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
78  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
79  if (I == map.end())
80    return None;
81  return I->second;
82}
83
84//------------------------------------------------------------------------====//
85// CFGBlockValues: dataflow values for CFG blocks.
86//====------------------------------------------------------------------------//
87
88// These values are defined in such a way that a merge can be done using
89// a bitwise OR.
90enum Value { Unknown = 0x0,         /* 00 */
91             Initialized = 0x1,     /* 01 */
92             Uninitialized = 0x2,   /* 10 */
93             MayUninitialized = 0x3 /* 11 */ };
94
95static bool isUninitialized(const Value v) {
96  return v >= Uninitialized;
97}
98static bool isAlwaysUninit(const Value v) {
99  return v == Uninitialized;
100}
101
102namespace {
103
104typedef llvm::PackedVector<Value, 2, llvm::SmallBitVector> ValueVector;
105
106class CFGBlockValues {
107  const CFG &cfg;
108  SmallVector<ValueVector, 8> vals;
109  ValueVector scratch;
110  DeclToIndex declToIndex;
111public:
112  CFGBlockValues(const CFG &cfg);
113
114  unsigned getNumEntries() const { return declToIndex.size(); }
115
116  void computeSetOfDeclarations(const DeclContext &dc);
117  ValueVector &getValueVector(const CFGBlock *block) {
118    return vals[block->getBlockID()];
119  }
120
121  void setAllScratchValues(Value V);
122  void mergeIntoScratch(ValueVector const &source, bool isFirst);
123  bool updateValueVectorWithScratch(const CFGBlock *block);
124
125  bool hasNoDeclarations() const {
126    return declToIndex.size() == 0;
127  }
128
129  void resetScratch();
130
131  ValueVector::reference operator[](const VarDecl *vd);
132
133  Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
134                 const VarDecl *vd) {
135    const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
136    assert(idx.hasValue());
137    return getValueVector(block)[idx.getValue()];
138  }
139};
140} // end anonymous namespace
141
142CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
143
144void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
145  declToIndex.computeMap(dc);
146  unsigned decls = declToIndex.size();
147  scratch.resize(decls);
148  unsigned n = cfg.getNumBlockIDs();
149  if (!n)
150    return;
151  vals.resize(n);
152  for (unsigned i = 0; i < n; ++i)
153    vals[i].resize(decls);
154}
155
156#if DEBUG_LOGGING
157static void printVector(const CFGBlock *block, ValueVector &bv,
158                        unsigned num) {
159  llvm::errs() << block->getBlockID() << " :";
160  for (unsigned i = 0; i < bv.size(); ++i) {
161    llvm::errs() << ' ' << bv[i];
162  }
163  llvm::errs() << " : " << num << '\n';
164}
165#endif
166
167void CFGBlockValues::setAllScratchValues(Value V) {
168  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
169    scratch[I] = V;
170}
171
172void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
173                                      bool isFirst) {
174  if (isFirst)
175    scratch = source;
176  else
177    scratch |= source;
178}
179
180bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
181  ValueVector &dst = getValueVector(block);
182  bool changed = (dst != scratch);
183  if (changed)
184    dst = scratch;
185#if DEBUG_LOGGING
186  printVector(block, scratch, 0);
187#endif
188  return changed;
189}
190
191void CFGBlockValues::resetScratch() {
192  scratch.reset();
193}
194
195ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
196  const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
197  assert(idx.hasValue());
198  return scratch[idx.getValue()];
199}
200
201//------------------------------------------------------------------------====//
202// Worklist: worklist for dataflow analysis.
203//====------------------------------------------------------------------------//
204
205namespace {
206class DataflowWorklist {
207  PostOrderCFGView::iterator PO_I, PO_E;
208  SmallVector<const CFGBlock *, 20> worklist;
209  llvm::BitVector enqueuedBlocks;
210public:
211  DataflowWorklist(const CFG &cfg, PostOrderCFGView &view)
212    : PO_I(view.begin()), PO_E(view.end()),
213      enqueuedBlocks(cfg.getNumBlockIDs(), true) {
214        // Treat the first block as already analyzed.
215        if (PO_I != PO_E) {
216          assert(*PO_I == &cfg.getEntry());
217          enqueuedBlocks[(*PO_I)->getBlockID()] = false;
218          ++PO_I;
219        }
220      }
221
222  void enqueueSuccessors(const CFGBlock *block);
223  const CFGBlock *dequeue();
224};
225}
226
227void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
228  for (CFGBlock::const_succ_iterator I = block->succ_begin(),
229       E = block->succ_end(); I != E; ++I) {
230    const CFGBlock *Successor = *I;
231    if (!Successor || enqueuedBlocks[Successor->getBlockID()])
232      continue;
233    worklist.push_back(Successor);
234    enqueuedBlocks[Successor->getBlockID()] = true;
235  }
236}
237
238const CFGBlock *DataflowWorklist::dequeue() {
239  const CFGBlock *B = nullptr;
240
241  // First dequeue from the worklist.  This can represent
242  // updates along backedges that we want propagated as quickly as possible.
243  if (!worklist.empty())
244    B = worklist.pop_back_val();
245
246  // Next dequeue from the initial reverse post order.  This is the
247  // theoretical ideal in the presence of no back edges.
248  else if (PO_I != PO_E) {
249    B = *PO_I;
250    ++PO_I;
251  }
252  else {
253    return nullptr;
254  }
255
256  assert(enqueuedBlocks[B->getBlockID()] == true);
257  enqueuedBlocks[B->getBlockID()] = false;
258  return B;
259}
260
261//------------------------------------------------------------------------====//
262// Classification of DeclRefExprs as use or initialization.
263//====------------------------------------------------------------------------//
264
265namespace {
266class FindVarResult {
267  const VarDecl *vd;
268  const DeclRefExpr *dr;
269public:
270  FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
271
272  const DeclRefExpr *getDeclRefExpr() const { return dr; }
273  const VarDecl *getDecl() const { return vd; }
274};
275
276static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
277  while (Ex) {
278    Ex = Ex->IgnoreParenNoopCasts(C);
279    if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
280      if (CE->getCastKind() == CK_LValueBitCast) {
281        Ex = CE->getSubExpr();
282        continue;
283      }
284    }
285    break;
286  }
287  return Ex;
288}
289
290/// If E is an expression comprising a reference to a single variable, find that
291/// variable.
292static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
293  if (const DeclRefExpr *DRE =
294        dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
295    if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
296      if (isTrackedVar(VD, DC))
297        return FindVarResult(VD, DRE);
298  return FindVarResult(nullptr, nullptr);
299}
300
301/// \brief Classify each DeclRefExpr as an initialization or a use. Any
302/// DeclRefExpr which isn't explicitly classified will be assumed to have
303/// escaped the analysis and will be treated as an initialization.
304class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
305public:
306  enum Class {
307    Init,
308    Use,
309    SelfInit,
310    Ignore
311  };
312
313private:
314  const DeclContext *DC;
315  llvm::DenseMap<const DeclRefExpr*, Class> Classification;
316
317  bool isTrackedVar(const VarDecl *VD) const {
318    return ::isTrackedVar(VD, DC);
319  }
320
321  void classify(const Expr *E, Class C);
322
323public:
324  ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
325
326  void VisitDeclStmt(DeclStmt *DS);
327  void VisitUnaryOperator(UnaryOperator *UO);
328  void VisitBinaryOperator(BinaryOperator *BO);
329  void VisitCallExpr(CallExpr *CE);
330  void VisitCastExpr(CastExpr *CE);
331
332  void operator()(Stmt *S) { Visit(S); }
333
334  Class get(const DeclRefExpr *DRE) const {
335    llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
336        = Classification.find(DRE);
337    if (I != Classification.end())
338      return I->second;
339
340    const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl());
341    if (!VD || !isTrackedVar(VD))
342      return Ignore;
343
344    return Init;
345  }
346};
347}
348
349static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
350  if (Expr *Init = VD->getInit()) {
351    const DeclRefExpr *DRE
352      = dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
353    if (DRE && DRE->getDecl() == VD)
354      return DRE;
355  }
356  return nullptr;
357}
358
359void ClassifyRefs::classify(const Expr *E, Class C) {
360  // The result of a ?: could also be an lvalue.
361  E = E->IgnoreParens();
362  if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
363    const Expr *TrueExpr = CO->getTrueExpr();
364    if (!isa<OpaqueValueExpr>(TrueExpr))
365      classify(TrueExpr, C);
366    classify(CO->getFalseExpr(), C);
367    return;
368  }
369
370  FindVarResult Var = findVar(E, DC);
371  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
372    Classification[DRE] = std::max(Classification[DRE], C);
373}
374
375void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
376  for (auto *DI : DS->decls()) {
377    VarDecl *VD = dyn_cast<VarDecl>(DI);
378    if (VD && isTrackedVar(VD))
379      if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
380        Classification[DRE] = SelfInit;
381  }
382}
383
384void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
385  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
386  // is not a compound-assignment, we will treat it as initializing the variable
387  // when TransferFunctions visits it. A compound-assignment does not affect
388  // whether a variable is uninitialized, and there's no point counting it as a
389  // use.
390  if (BO->isCompoundAssignmentOp())
391    classify(BO->getLHS(), Use);
392  else if (BO->getOpcode() == BO_Assign)
393    classify(BO->getLHS(), Ignore);
394}
395
396void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
397  // Increment and decrement are uses despite there being no lvalue-to-rvalue
398  // conversion.
399  if (UO->isIncrementDecrementOp())
400    classify(UO->getSubExpr(), Use);
401}
402
403void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
404  // If a value is passed by const reference to a function, we should not assume
405  // that it is initialized by the call, and we conservatively do not assume
406  // that it is used.
407  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
408       I != E; ++I)
409    if ((*I)->getType().isConstQualified() && (*I)->isGLValue())
410      classify(*I, Ignore);
411}
412
413void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
414  if (CE->getCastKind() == CK_LValueToRValue)
415    classify(CE->getSubExpr(), Use);
416  else if (CStyleCastExpr *CSE = dyn_cast<CStyleCastExpr>(CE)) {
417    if (CSE->getType()->isVoidType()) {
418      // Squelch any detected load of an uninitialized value if
419      // we cast it to void.
420      // e.g. (void) x;
421      classify(CSE->getSubExpr(), Ignore);
422    }
423  }
424}
425
426//------------------------------------------------------------------------====//
427// Transfer function for uninitialized values analysis.
428//====------------------------------------------------------------------------//
429
430namespace {
431class TransferFunctions : public StmtVisitor<TransferFunctions> {
432  CFGBlockValues &vals;
433  const CFG &cfg;
434  const CFGBlock *block;
435  AnalysisDeclContext &ac;
436  const ClassifyRefs &classification;
437  ObjCNoReturn objCNoRet;
438  UninitVariablesHandler &handler;
439
440public:
441  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
442                    const CFGBlock *block, AnalysisDeclContext &ac,
443                    const ClassifyRefs &classification,
444                    UninitVariablesHandler &handler)
445    : vals(vals), cfg(cfg), block(block), ac(ac),
446      classification(classification), objCNoRet(ac.getASTContext()),
447      handler(handler) {}
448
449  void reportUse(const Expr *ex, const VarDecl *vd);
450
451  void VisitBinaryOperator(BinaryOperator *bo);
452  void VisitBlockExpr(BlockExpr *be);
453  void VisitCallExpr(CallExpr *ce);
454  void VisitDeclRefExpr(DeclRefExpr *dr);
455  void VisitDeclStmt(DeclStmt *ds);
456  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
457  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
458
459  bool isTrackedVar(const VarDecl *vd) {
460    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
461  }
462
463  FindVarResult findVar(const Expr *ex) {
464    return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
465  }
466
467  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
468    UninitUse Use(ex, isAlwaysUninit(v));
469
470    assert(isUninitialized(v));
471    if (Use.getKind() == UninitUse::Always)
472      return Use;
473
474    // If an edge which leads unconditionally to this use did not initialize
475    // the variable, we can say something stronger than 'may be uninitialized':
476    // we can say 'either it's used uninitialized or you have dead code'.
477    //
478    // We track the number of successors of a node which have been visited, and
479    // visit a node once we have visited all of its successors. Only edges where
480    // the variable might still be uninitialized are followed. Since a variable
481    // can't transfer from being initialized to being uninitialized, this will
482    // trace out the subgraph which inevitably leads to the use and does not
483    // initialize the variable. We do not want to skip past loops, since their
484    // non-termination might be correlated with the initialization condition.
485    //
486    // For example:
487    //
488    //         void f(bool a, bool b) {
489    // block1:   int n;
490    //           if (a) {
491    // block2:     if (b)
492    // block3:       n = 1;
493    // block4:   } else if (b) {
494    // block5:     while (!a) {
495    // block6:       do_work(&a);
496    //               n = 2;
497    //             }
498    //           }
499    // block7:   if (a)
500    // block8:     g();
501    // block9:   return n;
502    //         }
503    //
504    // Starting from the maybe-uninitialized use in block 9:
505    //  * Block 7 is not visited because we have only visited one of its two
506    //    successors.
507    //  * Block 8 is visited because we've visited its only successor.
508    // From block 8:
509    //  * Block 7 is visited because we've now visited both of its successors.
510    // From block 7:
511    //  * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
512    //    of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
513    //  * Block 3 is not visited because it initializes 'n'.
514    // Now the algorithm terminates, having visited blocks 7 and 8, and having
515    // found the frontier is blocks 2, 4, and 5.
516    //
517    // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
518    // and 4), so we report that any time either of those edges is taken (in
519    // each case when 'b == false'), 'n' is used uninitialized.
520    SmallVector<const CFGBlock*, 32> Queue;
521    SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
522    Queue.push_back(block);
523    // Specify that we've already visited all successors of the starting block.
524    // This has the dual purpose of ensuring we never add it to the queue, and
525    // of marking it as not being a candidate element of the frontier.
526    SuccsVisited[block->getBlockID()] = block->succ_size();
527    while (!Queue.empty()) {
528      const CFGBlock *B = Queue.pop_back_val();
529
530      // If the use is always reached from the entry block, make a note of that.
531      if (B == &cfg.getEntry())
532        Use.setUninitAfterCall();
533
534      for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
535           I != E; ++I) {
536        const CFGBlock *Pred = *I;
537        if (!Pred)
538          continue;
539
540        Value AtPredExit = vals.getValue(Pred, B, vd);
541        if (AtPredExit == Initialized)
542          // This block initializes the variable.
543          continue;
544        if (AtPredExit == MayUninitialized &&
545            vals.getValue(B, nullptr, vd) == Uninitialized) {
546          // This block declares the variable (uninitialized), and is reachable
547          // from a block that initializes the variable. We can't guarantee to
548          // give an earlier location for the diagnostic (and it appears that
549          // this code is intended to be reachable) so give a diagnostic here
550          // and go no further down this path.
551          Use.setUninitAfterDecl();
552          continue;
553        }
554
555        unsigned &SV = SuccsVisited[Pred->getBlockID()];
556        if (!SV) {
557          // When visiting the first successor of a block, mark all NULL
558          // successors as having been visited.
559          for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
560                                             SE = Pred->succ_end();
561               SI != SE; ++SI)
562            if (!*SI)
563              ++SV;
564        }
565
566        if (++SV == Pred->succ_size())
567          // All paths from this block lead to the use and don't initialize the
568          // variable.
569          Queue.push_back(Pred);
570      }
571    }
572
573    // Scan the frontier, looking for blocks where the variable was
574    // uninitialized.
575    for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
576      const CFGBlock *Block = *BI;
577      unsigned BlockID = Block->getBlockID();
578      const Stmt *Term = Block->getTerminator();
579      if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
580          Term) {
581        // This block inevitably leads to the use. If we have an edge from here
582        // to a post-dominator block, and the variable is uninitialized on that
583        // edge, we have found a bug.
584        for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
585             E = Block->succ_end(); I != E; ++I) {
586          const CFGBlock *Succ = *I;
587          if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
588              vals.getValue(Block, Succ, vd) == Uninitialized) {
589            // Switch cases are a special case: report the label to the caller
590            // as the 'terminator', not the switch statement itself. Suppress
591            // situations where no label matched: we can't be sure that's
592            // possible.
593            if (isa<SwitchStmt>(Term)) {
594              const Stmt *Label = Succ->getLabel();
595              if (!Label || !isa<SwitchCase>(Label))
596                // Might not be possible.
597                continue;
598              UninitUse::Branch Branch;
599              Branch.Terminator = Label;
600              Branch.Output = 0; // Ignored.
601              Use.addUninitBranch(Branch);
602            } else {
603              UninitUse::Branch Branch;
604              Branch.Terminator = Term;
605              Branch.Output = I - Block->succ_begin();
606              Use.addUninitBranch(Branch);
607            }
608          }
609        }
610      }
611    }
612
613    return Use;
614  }
615};
616}
617
618void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
619  Value v = vals[vd];
620  if (isUninitialized(v))
621    handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
622}
623
624void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
625  // This represents an initialization of the 'element' value.
626  if (DeclStmt *DS = dyn_cast<DeclStmt>(FS->getElement())) {
627    const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
628    if (isTrackedVar(VD))
629      vals[VD] = Initialized;
630  }
631}
632
633void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
634  const BlockDecl *bd = be->getBlockDecl();
635  for (const auto &I : bd->captures()) {
636    const VarDecl *vd = I.getVariable();
637    if (!isTrackedVar(vd))
638      continue;
639    if (I.isByRef()) {
640      vals[vd] = Initialized;
641      continue;
642    }
643    reportUse(be, vd);
644  }
645}
646
647void TransferFunctions::VisitCallExpr(CallExpr *ce) {
648  if (Decl *Callee = ce->getCalleeDecl()) {
649    if (Callee->hasAttr<ReturnsTwiceAttr>()) {
650      // After a call to a function like setjmp or vfork, any variable which is
651      // initialized anywhere within this function may now be initialized. For
652      // now, just assume such a call initializes all variables.  FIXME: Only
653      // mark variables as initialized if they have an initializer which is
654      // reachable from here.
655      vals.setAllScratchValues(Initialized);
656    }
657    else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
658      // Functions labeled like "analyzer_noreturn" are often used to denote
659      // "panic" functions that in special debug situations can still return,
660      // but for the most part should not be treated as returning.  This is a
661      // useful annotation borrowed from the static analyzer that is useful for
662      // suppressing branch-specific false positives when we call one of these
663      // functions but keep pretending the path continues (when in reality the
664      // user doesn't care).
665      vals.setAllScratchValues(Unknown);
666    }
667  }
668}
669
670void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
671  switch (classification.get(dr)) {
672  case ClassifyRefs::Ignore:
673    break;
674  case ClassifyRefs::Use:
675    reportUse(dr, cast<VarDecl>(dr->getDecl()));
676    break;
677  case ClassifyRefs::Init:
678    vals[cast<VarDecl>(dr->getDecl())] = Initialized;
679    break;
680  case ClassifyRefs::SelfInit:
681      handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
682    break;
683  }
684}
685
686void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
687  if (BO->getOpcode() == BO_Assign) {
688    FindVarResult Var = findVar(BO->getLHS());
689    if (const VarDecl *VD = Var.getDecl())
690      vals[VD] = Initialized;
691  }
692}
693
694void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
695  for (auto *DI : DS->decls()) {
696    VarDecl *VD = dyn_cast<VarDecl>(DI);
697    if (VD && isTrackedVar(VD)) {
698      if (getSelfInitExpr(VD)) {
699        // If the initializer consists solely of a reference to itself, we
700        // explicitly mark the variable as uninitialized. This allows code
701        // like the following:
702        //
703        //   int x = x;
704        //
705        // to deliberately leave a variable uninitialized. Different analysis
706        // clients can detect this pattern and adjust their reporting
707        // appropriately, but we need to continue to analyze subsequent uses
708        // of the variable.
709        vals[VD] = Uninitialized;
710      } else if (VD->getInit()) {
711        // Treat the new variable as initialized.
712        vals[VD] = Initialized;
713      } else {
714        // No initializer: the variable is now uninitialized. This matters
715        // for cases like:
716        //   while (...) {
717        //     int n;
718        //     use(n);
719        //     n = 0;
720        //   }
721        // FIXME: Mark the variable as uninitialized whenever its scope is
722        // left, since its scope could be re-entered by a jump over the
723        // declaration.
724        vals[VD] = Uninitialized;
725      }
726    }
727  }
728}
729
730void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
731  // If the Objective-C message expression is an implicit no-return that
732  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
733  if (objCNoRet.isImplicitNoReturn(ME)) {
734    vals.setAllScratchValues(Unknown);
735  }
736}
737
738//------------------------------------------------------------------------====//
739// High-level "driver" logic for uninitialized values analysis.
740//====------------------------------------------------------------------------//
741
742static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
743                       AnalysisDeclContext &ac, CFGBlockValues &vals,
744                       const ClassifyRefs &classification,
745                       llvm::BitVector &wasAnalyzed,
746                       UninitVariablesHandler &handler) {
747  wasAnalyzed[block->getBlockID()] = true;
748  vals.resetScratch();
749  // Merge in values of predecessor blocks.
750  bool isFirst = true;
751  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
752       E = block->pred_end(); I != E; ++I) {
753    const CFGBlock *pred = *I;
754    if (!pred)
755      continue;
756    if (wasAnalyzed[pred->getBlockID()]) {
757      vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
758      isFirst = false;
759    }
760  }
761  // Apply the transfer function.
762  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
763  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
764       I != E; ++I) {
765    if (Optional<CFGStmt> cs = I->getAs<CFGStmt>())
766      tf.Visit(const_cast<Stmt*>(cs->getStmt()));
767  }
768  return vals.updateValueVectorWithScratch(block);
769}
770
771/// PruneBlocksHandler is a special UninitVariablesHandler that is used
772/// to detect when a CFGBlock has any *potential* use of an uninitialized
773/// variable.  It is mainly used to prune out work during the final
774/// reporting pass.
775namespace {
776struct PruneBlocksHandler : public UninitVariablesHandler {
777  PruneBlocksHandler(unsigned numBlocks)
778    : hadUse(numBlocks, false), hadAnyUse(false),
779      currentBlock(0) {}
780
781  virtual ~PruneBlocksHandler() {}
782
783  /// Records if a CFGBlock had a potential use of an uninitialized variable.
784  llvm::BitVector hadUse;
785
786  /// Records if any CFGBlock had a potential use of an uninitialized variable.
787  bool hadAnyUse;
788
789  /// The current block to scribble use information.
790  unsigned currentBlock;
791
792  void handleUseOfUninitVariable(const VarDecl *vd,
793                                 const UninitUse &use) override {
794    hadUse[currentBlock] = true;
795    hadAnyUse = true;
796  }
797
798  /// Called when the uninitialized variable analysis detects the
799  /// idiom 'int x = x'.  All other uses of 'x' within the initializer
800  /// are handled by handleUseOfUninitVariable.
801  void handleSelfInit(const VarDecl *vd) override {
802    hadUse[currentBlock] = true;
803    hadAnyUse = true;
804  }
805};
806}
807
808void clang::runUninitializedVariablesAnalysis(
809    const DeclContext &dc,
810    const CFG &cfg,
811    AnalysisDeclContext &ac,
812    UninitVariablesHandler &handler,
813    UninitVariablesAnalysisStats &stats) {
814  CFGBlockValues vals(cfg);
815  vals.computeSetOfDeclarations(dc);
816  if (vals.hasNoDeclarations())
817    return;
818
819  stats.NumVariablesAnalyzed = vals.getNumEntries();
820
821  // Precompute which expressions are uses and which are initializations.
822  ClassifyRefs classification(ac);
823  cfg.VisitBlockStmts(classification);
824
825  // Mark all variables uninitialized at the entry.
826  const CFGBlock &entry = cfg.getEntry();
827  ValueVector &vec = vals.getValueVector(&entry);
828  const unsigned n = vals.getNumEntries();
829  for (unsigned j = 0; j < n ; ++j) {
830    vec[j] = Uninitialized;
831  }
832
833  // Proceed with the workist.
834  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
835  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
836  worklist.enqueueSuccessors(&cfg.getEntry());
837  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
838  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
839  PruneBlocksHandler PBH(cfg.getNumBlockIDs());
840
841  while (const CFGBlock *block = worklist.dequeue()) {
842    PBH.currentBlock = block->getBlockID();
843
844    // Did the block change?
845    bool changed = runOnBlock(block, cfg, ac, vals,
846                              classification, wasAnalyzed, PBH);
847    ++stats.NumBlockVisits;
848    if (changed || !previouslyVisited[block->getBlockID()])
849      worklist.enqueueSuccessors(block);
850    previouslyVisited[block->getBlockID()] = true;
851  }
852
853  if (!PBH.hadAnyUse)
854    return;
855
856  // Run through the blocks one more time, and report uninitialized variables.
857  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
858    const CFGBlock *block = *BI;
859    if (PBH.hadUse[block->getBlockID()]) {
860      runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
861      ++stats.NumBlockVisits;
862    }
863  }
864}
865
866UninitVariablesHandler::~UninitVariablesHandler() {}
867